Cultivation and reduced-rate herbicides for cost-effective weed control in sugarbeet grown for biofuel

Authors: Johnson, Wiley - Carroll; Webster, Theodore; GREY, TIMOTHY - University Of Georgia; LUO, XUELIN - University Of Georgia

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2018
Publication Date: 12/1/2018
Citation: Johnson, W.C., Webster, T.M., Grey, T.L., Luo, X. 2018. Cultivation and reduced-rate herbicides for cost-effective weed control in sugarbeet grown for biofuel. Weed Technology. 32(6):726-732. https://doi.org/10.1017/wet.2018.61.
DOI: https://doi.org/10.1017/wet.2018.61

Interpretive Summary: Sugarbeet, grown for biofuel, is being considered as an alternate cool-season crop in the southeastern U. S. coastal plain. Previous research identified ethofumesate (Nortron®) PRE and phenmedipham + desmedipham (Betamix®) POST as herbicides that controlled troublesome cool-season weeds in the region, specifically cutleaf eveningprimrose. Ethofumesate and phenmedipham + desmedipham are used on sugarbeet grown for edible sugar, a subsidized specialty crop, and the herbicides are priced accordingly. Since sugarbeet would be grown as a biofuel in the southeastern U. S., production budgets would likely be based on less costly forms of weed control compared to sugarbeet grown for edible sugar. Research trials were conducted for three seasons from 2014 through the 2016 to evaluate sweep cultivation and reduced rates of ethofumesate PRE and/or phenmedipham + desmedipham POST for cost-effective weed control in sugarbeet grown for biofuel. Cultivation improved control of cool-season weeds, but the effect was independent of control provided by herbicides. Of the herbicide combinations evaluated, the best overall cool-season weed control was from systems that included either a 1/2X or 1X rate of phenmedipham + desmedipham POST. Either rate of ethofumesate PRE was less effective than phenmedipham + desmedipham POST. Surprisingly, despite improved weed control, sugarbeet yield was not affected by cultivation each year of the study. In contrast, sugarbeet yield response to herbicides was similar to weed control response. These results indicate that for cool-season weed control in sugarbeet grown for biofuel, cultivation has a very limited role. The theory of cost-effective weed control based on cultivation combined with reduced herbicide rates does not appear to be viable for sugarbeet grown for biofuel.

Technical Abstract: Sugarbeet, grown for biofuel, is being considered as an alternate cool-season crop in the southeastern U. S. coastal plain. Previous research identified ethofumesate PRE and phenmedipham + desmedipham POST as herbicides that controlled troublesome cool-season weeds in the region, specifically cutleaf eveningprimrose. Ethofumesate and phenmedipham + desmedipham are used on sugarbeet grown for edible sugar, a subsidized specialty crop, and the herbicides are priced accordingly. Since sugarbeet would be grown as a biofuel in the southeastern U. S., production budgets would likely be based on less costly forms of weed control compared to sugarbeet grown for edible sugar. Research trials were conducted for three seasons from 2014 through the 2016 to evaluate sweep cultivation and reduced rates of ethofumesate PRE and/or phenmedipham + desmedipham POST for cost-effective weed control in sugarbeet grown for biofuel. There were no interactions between the main-effects of cultivation and herbicides used for control of cutleaf eveningprimrose and other cool-season species two years of three. Cultivation improved control of cool-season weeds, but the effect was independent of control provided by herbicides. Of the herbicide combinations evaluated, the best overall cool-season weed control was from systems that included either a 1/2X or 1X rate of phenmedipham + desmedipham POST. Either rate of ethofumesate PRE was less effective than phenmedipham + desmedipham POST. Surprisingly, despite improved weed control, sugarbeet yield was not affected by cultivation each year of the study. In contrast, sugarbeet yields were greater when treated with any herbicide combination that included either a 1/2X or 1X rate of phenmedipham + desmedipham POST compared to either rate of ethofumesate PRE alone or the nontreated control. These results indicate that for cool-season weed control in sugarbeet grown for biofuel, cultivation has a very limited role. The premise of cost-effective weed control based on cultivation combined with reduced herbicide rates does not appear to be viable for sugarbeet grown for biofuel.